on as to the
quantity of lime required to correct the acidity.

This test is simple and inexpensive, and at the present time most county
agent offices are equipped with this apparatus or a similar one for
testing soils for farmers. Some newer methods are being devised, and
doubtless this method will be improved upon as time passes, but the
Truog test has qualities of accuracy and simplicity which will always
make it valuable.

CHAPTER VI

SOURCES OF LIME

_Nature's Provision._ Soils are composed of pulverized stone and organic
matter. Much of the original stone contained little lime, and the human
race would become nearly helpless if there were no stores of supply in
the form of limestone, chalk, marl, etc. The day would come when the
surface soil could not produce our staple crops if its loss of lime
continued, and a means of replenishing the stock were not at hand. The
huge deposits of limestone that have not been disintegrated by processes
of weathering are assurance that the soil's need can be met forever. The
calcium and magnesium in the stone are in chemical combination with
carbonic acid forming carbonates, and there is an additional mixture of
other earthy material that was deposited by the water when the stone was
being formed, but much limestone possesses an excellent degree of
purity.

[Illustration: Lime Favors Clover at the Ohio Experiment Station]

[Illustration: Lime Affects Growth of Corn at the Ohio Experiment
Station]

_Confusion Respecting Forms._ In the public mind there is much confusion
respecting the sources and forms of lime most to be desired. Wood
ashes appealed to people, especially in an early day in our agriculture,
partly because the ashes were so universally present that tests had been
made voluntarily and otherwise in millions of instances. The value of
such tests had been obscured by the fact that the ashes contained
potash, and much of the credit of any good effect was attributed to that
fact. It has been generally known, however, that lime in peculiarly
effective form is in wood ashes, and the favor in which ashes have been
held rested not a little upon the curious preference for an organic
source of all soil amendments. This is seen in the case of direct
fertilizers.

_Dealers' Interests._ The doubts regarding the wisdom of selecting any
one form of lime for the betterment of soil conditions have been
promoted very naturally by the conflicting interests of men who w